Clone this repo and run make. (You also need npm: run brew install npm if you don't have it already.)
jq-agg lets you write filters in the "jq" language and execute them in MongoDB using the aggregation framework.
jq is "like sed for JSON": it lets you explore and transform JSON easily, the way sed and grep do for text. For example, this query finds the most populous US state that starts with the letter "A":
$ mongoexport -c zips | jq -s ' map(select(.state > "B")) | group_by(.state; {p: map(.pop)|add}) | max_by(.p) '
jq-agg lets you run jq queries directly in the mongo shell. For example, you can run the previous query like this:
> db.zips.jq(' map(select(.state > "B")) | group_by(.state; {p: map(.pop)|add}) | max_by(.p) ')
Internally, the jq query is rewritten into a MongoDB aggregation query. Like any agg query, you can explain it to see what indexes and pipeline stages it uses:
> db.zips.explain().jq(' map(select(.state > "B")) | group_by(.state; {p: map(.pop)|add}) | max_by(.p) ')